<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        var age=prompt('请输入你的年龄');
        var str='您今年已经'+age+'岁了';
        alert(str);

    </script>
</head>
<body>

</body>
</html>